White spot syndrome virus in decapods from Mississippi Sound, USA, and susceptibility of Palaemonetes pugio and Uca panacea to a Chinese isolate

The presence and quantity of white spot syndrome virus (WSSV) was surveyed using TaqMan real-time PCR to assess the extent of the virus in Mississippi Sound, USA. A total of 3577 wild decapods comprising 11 species was collected between November 2012 and August 2015: WSSV was present in 10 of the 11 species. Prevalence ranged from 5.1% in Uca rapax to 38.8% in U. spinicarpa. Viral load ranged from 1.8 to 7.3 log10 copies of WSSV µg-1 total DNA. Two Gulf species, Palaemonetes pugio and U. panacea, were injected with a series of doses of a virulent WSSV isolate from China to determine relative susceptibility and virulence because continuing translocation of highly pathogenic isolates of WSSV poses risk to native species. Survival was 0-65% for P. pugio and 5-60% for U. panacea. Median survival time was lower for P. pugio than U. panacea at all doses. Mean (±SD) lethal load was 9.0 ± 8.9 log copies of WSSV µg-1 total DNA in P. pugio and 8.2 ± 8.3 in U. panacea. Mean viral load in survivors was higher in U. panacea than in P. pugio (5.8 ± 6.1 vs. 3.2 ± 3.0 log copies of WSSV µg-1 total DNA); mean viral load was lower in wild individuals of those species (2.9 ± 3.2 for P. pugio and 4.9 ± 5.0 for U. panacea). U. panacea is potentially more tolerant of WSSV than P. pugio and may serve as an important reservoir host in the community.

Developmental Dynamics of Green Fluorescent Chromatophores in the Daggerblade Grass Shrimp, Palaemonetes Pugio Holthuis, 1949 (Decapoda, Caridea, Palaemonidae)

ABSTRACTThe daggerblade grass shrimp, Palaemonetes pugio Holthuis 1949 relies heavily on transparency as the primary form of camouflage yet possess several types of pigmented chromatophores located throughout the body. A distinct sub-population of yellow/white chromatophores have been discovered to exhibit brilliant green fluorescence. These cells develop in the embryo and are the primary chromatophore present in larval organisms. Post-larval grass shrimp undergo a major restructuring of the pattern and morphology of fluorescent chromatophores after metamorphosis with chromatophores found uniformly distributed throughout the body and at high concentration on the hepatopancreas and the eye stalks. In adult P. pugio the number of fluorescent chromatophores is significantly reduced and fluorescence is limited to only a subset of these chromatophores. The novel fluorescent properties of these cells, there relatively high abundance during early life stages, and pattern of development, suggest important cellular functions for these fluorescent chromatophores in grass shrimp.

The effects of the parasite Probopyrus pandalicola (Packard, 1879) (Isopoda, Bopyridae) on the behavior, transparent camouflage, and predators of Palaemonetes pugio Holthuis, 1949 (Decapoda, Palaemonidae)

The bopyrid isopod Probopyrus pandalicola (Packard, 1879) is a large, noticeable, hematophagous ectoparasite of palaemonid shrimps, including the daggerblade grass shrimp Palaemonetes pugio Holthuis, 1949. Bopyrids affect grass shrimp physiology and may also affect predator-prey dynamics. The purpose of this study was to determine whether the isopod affected the behavior and/or camouflage of grass shrimp, thereby altering the predation preferences of the mummichog Fundulus heteroclitus (Linnaeus, 1766). To determine whether the isopod affected predator preference through behavioral and/or camouflage alterations, paired combinations of unparasitized, parasitized, and marked shrimp were presented to mummichogs. One branchiostegite of some of the unparasitized shrimp was marked with black paint to mimic the bopyrid parasite. Mummichog predation preference and shrimp behavior immediately prior to predation events were recorded. All shrimp behavior was classified as motionless, walking, swimming, or backward thrusting. Immediately prior to predation, parasitized shrimp swam more () and backward thrusted less () than unparasitized shrimp. Mummichogs exhibited a preference for the more active shrimp (80.7% of shrimp; ), and also for the less camouflaged (parasitized or marked) shrimp (81.5% of shrimp; ) if there was no difference in shrimp behavior. Parasitized shrimp were preferentially consumed (51/85 shrimp) when paired with unparasitized shrimp (), but not with marked shrimp (). A 30-min activity budget was created for each type of shrimp both in the presence and absence of predators; neither the parasite nor marking affected their behavior over 30 min (). The major finding of this study was that P. pandalicola affected the predation preferences of F. heteroclitus by altering the behavior and/or camouflage of the grass shrimp. Parasitization alters predator-prey dynamics by decreasing the camouflage and the frequency of backward-thrusting behavior by the host when it is threatened by predation, which thereby decreases the ability of shrimp to escape from predators.